I am very disappointed by the behavior of the community in this thread, because I believe that there is probably an easy workaround, but it hasn’t been discovered.
There are quite a few credible posts by users who experience no problems with HomeKit integration. And there is clearly some selection bias – most users without HomeKit issues will not have posted in or even visited this thread. Let’s say (for example) that half the HomeKit users have trouble with frequent disconnects and half don’t. If we find out what the difference is, we can change the failing systems so they work reliably.
IMO, it’s very unlikely that the ‘bad’ units have a hardware defect. It could be a firmware version difference, back-end data issue, etc., but I believe that the most likely cause is controller firmware that is intolerant of certain Wi-Fi AP or router/firewall behavior. With luck, most users will be able to fix this with a settings change. If their APs have a quirk that can’t be configured away, maybe adding the right $25 AP will work. Or, perhaps you wanted to upgrade your Wi-Fi anyhow; choose new APs that are compatible with the present firmware.